Nitrate reductase

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Werner M. Kaiser, Steven C. Assimilatory nitrate reductase NR of higher plants is a most interesting enzyme, both from its central function in plant primary metabolism and from the complex regulation of its expression and control of catalytic activity and degradation. It is also demonstrated that stress factors like nitrate deficiency and salinity have remarkably little direct influence on the NR activation state. Further, changes in NR activity measured in vitro are not always associated with changes in nitrate reduction rates in vivo , suggesting that NR can be under strong substrate limitation. However, it is not known whether the molecular form of NR in vivo affects its susceptibility to proteolytic degradation, or whether factors that affect the NR activation state also independently affect the activity or induction of the NR protease s.

Nitrate reductase

Nitrate reductase NR is the first enzyme of the nitrogen reduction pathway in plants, leading to the production of ammonia. However, in the nitrogen-fixing symbiosis between legumes and rhizobia, atmospheric nitrogen N 2 is directly reduced to ammonia by the bacterial nitrogenase, which questions the role of NR in symbiosis. Next to that, NR is the best-characterized source of nitric oxide NO in plants, and NO is known to be produced during the symbiosis. Moreover, NRs are involved together with the mitochondrial electron transfer chain in NO production throughout the symbiotic process and energy regeneration in N 2 -fixing nodules. Using an in vivo NMR spectrometric approach, we show that, in mature nodules, NRs participate also in the regulation of energy state, cytosolic pH, carbon and nitrogen metabolism under both normoxia and hypoxia. These data point to the importance of NR activity for the N 2 -fixing symbiosis and provide a first explanation of its role in this process. In plants, yeasts, algae, and fungi, nitrate reductase NR is a key enzyme of the nitrogen N reduction and assimilation pathway. However, many studies have reported high NR expression and activity in symbiotic nodules see Streeter, a ; Streeter, b ; Arrese-Igor et al. The involvement of NR activity in NO production has been evidenced in many plant organs and tissues over the past 20 years Dean and Harper, ; Yamasaki and Sakihama, ; Rockel et al. Although the interaction between NR and NOFNiR has been argued in eukaryotic algae, the proof of concept in higher plant is still not demonstrated. NO is a reactive free radical gaseous molecule with a broad spectrum of regulatory functions in plant growth and development, and in response to abiotic and biotic factors Kolbert et al. NO is particularly involved in the legume—Rhizobium symbiotic interactions Hichri et al.

Transduction of NO-bioactivity by the red blood cell in sepsis: novel mechanisms of vasodilation during acute inflammatory disease.

This reaction is critical for the production of protein in most crop plants, as nitrate is the predominant source of nitrogen in fertilized soils. Eukaryotic nitrate reductases are part of the sulfite oxidase family of molybdoenzymes. Prokaryotic nitrate reductases belong to the DMSO reductase family of molybdoenzymes and have been classified into three groups, assimilatory nitrate reductases Nas , respiratory nitrate reductase Nar , and periplasmic nitrate reductases Nap. In Nap, the molybdenum is covalently attached to the protein by a cysteine side chain, and an aspartate side chain in Nar. Prokaryotic nitrate reductases have two major types, transmembrane nitrate reductases NAR and periplasmic nitrate reductases NAP.

Thank you for visiting nature. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser or turn off compatibility mode in Internet Explorer. In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript. Nitrate is generally considered a water pollutant and an undesirable fertilizer residue in the food chain. Research in the s indicated that, by reducing nitrate to nitrite, commensal bacteria might be involved in the pathogenesis of gastric cancers and other malignancies, as nitrite can enhance the generation of carcinogenic N -nitrosamines.

Nitrate reductase

Nitrate NO 3 is a nitrogen-containing molecule that can be reduced by some bacterial species, but not others. Therefore, examining the ability of bacterial species to conduct nitrogen reduction is useful for characterizing and identifying bacterial species. Reduction of nitrate generally occurs during anaerobic respiration in which an organism derives its oxygen from nitrate to serve as the final electron acceptor to remove electrons from the electron transport chain.

Terri telle md

NapG contains four iron sulfur binding motifs and is associated with the periplasmic face of the membrane. Access through your institution. Meilhoc, E. Hardy, R. Sproules S, Wieghardt K. Interestingly, our study shows that over a short period of time, i. Structural characterization of the E. Mutants or transformants disturbed in that transport may add to a better understanding of the substrate limitations of NR. Non-enzymatic nitric oxide synthesis in biological systems. Her research interests center on metabolism and signaling of nitrogen oxyanions nitrate, nitrite, and nitric oxide in human vascular diseases and pathogenic bacteria. However, this was not the case. In principle, spectroscopic characterization of different species in the catalytic cycle should help in delineating their electronic structure, which ultimately controls the reactivity. Oxidoreductases : nitrogenous donor EC 1. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

The periplasmic nitrate reductase NapAB from Cupriavidus necator is a heterodimeric protein that belongs to the dimethyl sulfoxide reductase family of mononuclear Mo-containing enzymes and catalyzes the reduction of nitrate to nitrite.

As far as is known, there is only one exception: NR in leaves from Ricinus communis L. The species giving this signal is also considered to be inactive. Enzymes Redox partner reactions Potentials mV Ref. The alignment of the C. A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Li, H. Faraday Discuss. Humans naturally ingest nitrate through diet as it is found in meat, fruits, vegetables, grains, dairy products, and drinking water. Based on a detailed analysis of the conformation of the pterin cofactor as determined from crystallography, Rothery et al. Wageningen University, PhD thesis. Glutamine synthetase in Medicago truncatula, unveiling new secrets of a very old enzyme.